Organic cation diffusion in root cell walls of different plants

Abstract

A comparative study of the uptake of cation type dye (methylene blue) of the isolated root cell walls and of the roots of whole transpirating seedlings was performed. Seven day seedlings of the Triticum aestivum L., Zea mays L., Cucumis sativus L., Lupinus albus L. and Vigna radiata L. grown at low concentration of all nutrients (~0.2 mM) in the medium were used. We determined the amount of ionogenic groups per 1 g of dry and fresh weight of root cell walls, their swelling capacity, ion exchange capacity on methylene blue (Mcw) depending on adsorption time and diffusion coefficients of organic cation into the polymeric matrix of cell walls (Dcw). It was shown that both Mcw depended on šĶ (or dissociation degree of the carboxyl groups), changed in accordance with the amount of the carboxyl groups per 1 g of cell walls dry weight and decreased as follows: cucumber > mungbean > lupin > wheat >corn. The results indicate that Dcw also depended on plant species and decreased in the order: lupin > mungbean > maize > cucumber > wheat. We conclude that the mechanism of methylene blue absorption by plant root cell walls is stimulated by ion exchange reactions between the methylene blue cation and carboxyl groups of cell walls, but the rate of absorption is mainly defined by methylene blue cation diffusion into the cell wall polymeric matrix. Keywords: coefficients of diffusion, cell walls, roots, dye uptake